The core leader, Dr. Dikalov, is an expert in in vitro and ex vivo measurements of ROS and NO in vascular cells and tissues and has been at the forefront in developing new methodologies for ROS detection using ESR spectroscopy. Much of his work has been focused on development of new ESR techniques for in vitro and in vivo measurements of ROS (12-14). While ESR spectroscopy can directly detect free radical products, most biologically relevant radicals are far too short-lived to be detected in biological specimens. For this reason, spin-trapping and spin probes have been used. Spin trapping has proven to be one of the most definitive^ methods for ROS detection and quantification. CORE A has published extensively on spin trapping of O2~ and NO using nitrone spin traps and Fe(DETC)2 (15-17). Moreover, Dr. Dikalov and colleagues at the Institute of Organic Chemistry in Novosibirsk, Russia have designed and validated a variety of new cyclic hydroxylamines which act as spin probes that provide enhanced sensitivity for ROS detection (14, 18). The focus of Core A will be the ROS and NO in cultured cells and intact tissue samples. Dr. Dikalov has also developed an approach to measure the production of hydrogen peroxide (H2O2) in membrane fractions using a peroxidase-mediated oxidation of CPH. In addition, the Electron Spin Resonance Core will develop new methods and refine existing techniques for measurements of ROS in relevant tissues. The application of these methods will enhance the ability of the individual project leaders to test their hypotheses and design new studies as necessary to advance their work.